bit field

// <Pointer on C> by Kenneth A. Reek
// P89
// No.5
 
int store_bit_field(int original_value, int value_to_store, unsigned starting_bit, unsigned ending_bit)
{
	unsigned int mask = ~0;
	int n_bits = sizeof(unsigned int) * 8;
	mask <<= (n_bits - 1 - starting_bit) ;
	mask >>= (n_bits - (starting_bit - ending_bit + 1));
	mask <<= ending_bit;
 
	return (original_value & ~mask) | ((value_to_store << ending_bit) & mask);
}
 
int main (int argc, char const *argv[])
{
	printf("%xn", store_bit_field(0x0, 0x1, 4, 4));
	printf("%xn", store_bit_field(0xffff, 0x123, 15, 4));
	printf("%xn", store_bit_field(0xffff, 0x123, 13, 9));
	return 0;
}